This invention relates to an ethylene copolymer rubber composition, more particularly to an ethylene copolymer rubber composition excellent in processing characteristics which have been the problem of an ethylene copolymer rubber produced with a metallocene catalyst, and also excellent in balance between the processing characteristics and mechanical and low-temperature characteristics. It relates also to an ethylene copolymer rubber composition in which a conjugated diene rubber is blended with the above-mentioned ethylene copolymer rubber, which is excellent in processing characteristics and co-vulcanizability with a conjugated diene rubbers
Ethylene/.alpha.-olefin/non-conjugated diene copolymers are excellent in weather resistance, heat resistance, cold resistance, ozone resistance and the like, and have heretofore been widely used in constructive materials, automobile parts, wire-coating materials and the like.
Moreover, in recent years, there have been made many proposals of the production of an ethylene/.alpha.-olefin/non-conjugated diene copolymer obtained with a metallocene catalyst. The metallocene catalyst is excellent in copolymerizability of comonomers such as ethylene, an .alpha.-olefin, a non-conjugated diene and the like; has such characteristics that the molecular weight distribution of a polymer obtained is narrow and the composition distribution is uniform and the like; and also has such characteristics that even comonomers (for example, long chain .alpha.-olefins) which have been difficult to polymerize with a vanadium catalyst which has been a conventional polymerization catalyst for producing an ethylene/.alpha.-olefin/non-conjugated diene copolymer, can be easily polymerized.
In, for example, JP-B-5('93)-80,493, there is proposed a low-crystalline, ethylenic random copolymer in which the content of each of ethylene, .alpha.-olefin having 3 to 10 carbon atoms and non-conjugated diene is specified, each of intrinsic viscosity, molecular weight distribution (M.sub.w /M.sub.n), crystallinity, B value relevant to the mole fraction of .alpha.-olefin-ethylene chain and amount of a boiling methyl acetate-soluble portion is also specified, and neither .alpha..beta. signal nor .beta..gamma. signal based on the methylene chain between two adjacent tertiary carbon atoms are observed in the .sup.13 C-NMR spectrum.
As to a vulcanized rubber obtained from the above copolymer, mechanical characteristics such as modulus, tensile strength, elongation at break, hardness and the like have been examined; but the inherent characteristics of the ethylene/.alpha.-olefin/non-conjugated diene copolymer including processing characteristics, low-temperature characteristics and the like in addition to the above mechanical characteristics have not been collectively examined.
Furthermore, the present inventors have recently proposed in JP-A-2('90)-51512 a process for improving the co-vulcanizability of an ethylene/.alpha.-olefin/non-conjugated diene copolymer rubber with a conjugated diene rubber using a straight chain, non-conjugated diene, a representative of which is 7-methyl-1,6-octadiene, said process being higher in vulcanization rate than when 5-ethylidene-2-norbornene is used. In JP-A-5('93)-262827, it is disclosed that an ethylene/.alpha.-olefin/7-methyl-1,6-octadiene copolymer rubber obtained with a metallocene catalyst is excellent in low-temperature characteristics, and in JP-A-6-128427, it is disclosed that a blend composition of a conjugated diene rubber with an ethylene/.alpha.-olefin/7-methyl-1,6-octadiene copolymer obtained with a metallocene catalyst has an improved co-vulcanizability.
However, originally, the ethylene/.alpha.-olefin/non-conjugated diene copolymer and the conjugated diene rubber are inferior in compatibility with each other and the ethylene/.alpha.-olefin/non-conjugated diene copolymer obtained with a metallocene catalyst has a narrow molecular weight distribution, and hence, has such a disadvantage that the processability is inferior. Therefore, when it is kneaded by a Banbury mixer or the like, it does not well mix with the conjugated diene rubber. Thus, a rubber composition containing the conventional ethylene/.alpha.-olefin/non-conjugated diene copolymer has not been sufficiently satisfactory in processing characteristics.
On the other hand, as a method of improving the processing characteristics of a polymer obtained with a metallocene catalyst, there has been considered a method of combining a low molecular weight copolymer with a high molecular weight copolymer which is different in composition from the low molecular weight copolymer, and as a specific example thereof, there are mentioned a multistage method in which several reactors for producing the copolymer are connected in series and the polymerization is effected continuously, a method in which at least two catalysts different in reactivity are charged into a reactor, and the like. However, these methods have such problems that the productivity is low, which causes an increase in cost, the control of polymerization is difficult and the like. Therefore, the above methods cannot be said to be advisable in industry.